CVE
Heym: Command execution via POST /api/mcp/fetch-tools stdio transport: supplied command is spawned before MCP validation
- Exploited
- No known exploitation
- Fix
- Fixed in 0.0.75
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. The MCP stdio transport is reachable on POST /api/mcp/fetch-tools in Heym versions up to and including 0.0.75. The transport defaults to stdio when the request does not set one.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 17/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Heym, a self-hosted platform for building agentic systems and business-process automations, has a flaw in its POST /api/mcp/fetch-tools endpoint that lets any logged-in user, including the lowest-privilege role, run an attacker-supplied command with arguments on the shared backend host. An attacker can reach it remotely with low-privilege credentials, and the command runs before MCP validation fails, so its side effects occur even if it does not speak MCP.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
Heym builds and runs agentic systems and business-process automations on self-hosted infrastructure. Prior to version 0.0.75, the same POST /api/mcp/fetch-tools endpoint (any authenticated user, lowest role) also accepts the stdio transport, which spawns the attacker-supplied command with attacker-supplied args and an environment merged over os.environ. The process executes on the shared backend host before MCP protocol validation fails — so side effects fire regardless of whether the command speaks MCP. This is a distinct weakness class and exploit primitive from the SSRF (Advisory 2) on the same endpoint, and needs a different fix (role gating / opt-in trust boundary rather than egress controls). This issue has been patched in version 0.0.75.
Who should check
Anyone running Heym 0.0.75 or earlier on a shared or multi-user backend where any authenticated user can reach the MCP fetch-tools endpoint.
Read the source excerpt
“The same POST /api/mcp/fetch-tools endpoint (any authenticated user, lowest role)”
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure8/25Specific setups only, reachable over the network
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.8/10CVSS 8.8
- No patch0/5No signal
What would change the score
- Would score about 67 if added to CISA KEV
- Would score about 62 if CISA's SSVC rates exploitation active
- Would score about 24 if CISA's SSVC rates it automatable
What to do
Check whether your setup matches what the bug needs.
The MCP stdio transport is reachable on POST /api/mcp/fetch-tools in Heym versions up to and including 0.0.75. The transport defaults to stdio when the request does not set one.Upgrade to a fixed version: 0.0.75.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-67546 (Heym: Command execution via POST /api/mcp/fetch-tools stdio transport: supplied command is spawned before MCP validation), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-67546 (entry last updated 2026-11-11):
Affected:
- heymrun heym: fixed in 0.0.75
Fixed versions: 0.0.75.
Conditions (all must be true for the bug to be hit):
- The MCP stdio transport is reachable on POST /api/mcp/fetch-tools in Heym versions up to and including 0.0.75. (source: https://github.com/heymrun/heym/security/advisories/GHSA-378x-q589-34mv)
- The transport defaults to stdio when the request does not set one. (source: https://github.com/heymrun/heym/security/advisories/GHSA-378x-q589-34mv)
Setup: the bug is reachable in a default setup; no special feature or setting is needed.
Attacker needs: network access, low-privilege login, no user action.
CISA KEV: CVE-2026-67546 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-67546 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/heymrun/heym/security/advisories/GHSA-378x-q589-34mv
- https://github.com/heymrun/heym/commit/22b8ee60eb92128cf4ff04a9b6c0e1b62bf25a01
- https://github.com/heymrun/heym/commit/6c6213f88dfa8b2a70d23a9a271171241e910904
- https://github.com/heymrun/heym/releases/tag/v0.0.75
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-67546
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-67546"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- heymrun heym
fixed in 0.0.75
Evidence 5
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
Other links · 3
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-67546
Is CVE-2026-67546 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
The endpoint POST /api/mcp/fetch-tools accepts an MCP stdio transport, and the supplied command is started before the request is validated as MCP. Any signed-in user, including the lowest role, can therefore run arbitrary commands on the shared backend host. The advisory notes this can lead to host root when combined with the docker.sock mount.Source: github.com
Which versions are affected by CVE-2026-67546?
heym: before 0.0.75.Source: cve.now feed data
Am I affected, and how do I check?
Heym versions up to and including 0.0.75 are affected when the MCP stdio transport is reachable on POST /api/mcp/fetch-tools. The transport defaults to stdio when a request does not set one, so check the Heym version you run against the fixed version 0.0.75.Source: github.com
How do I fix CVE-2026-67546?
Upgrade Heym to 0.0.75 or later, which contains the fix.Source: github.com